very cute! i wonder how long that tree will live without any soil.

I was wondering too. I have though, now & again, seen seedlings of various sorts growing out of the partly rotted trunks of fallen trees, so perhaps in this case, the log is, in effect, the soil.

There are other pictures of Japan at the website, though they're mostly not garden pictures - http://www.bigfoto.com/asia/japan/ - which makes me surmise that the log's placement isn't accidental & was intended as a place for the little turtles to climb onto.